Field of the Invention
The present invention relates to a radiation imaging apparatus, a driving method for the same, and a non-transitory computer-readable medium.
Description of the Related Art
A radiation imaging apparatus includes a plurality of sensors and a driving unit which drives the plurality of sensors. Each sensor includes, for example, a detection element for detecting radiation and a reset unit for initializing the detection element. A sensor signal output from each sensor contains a noise component originating from a dark current or the like in addition to a signal component corresponding to the radiation detected by the detection element. For this reason, before the start of radiation irradiation, the driving unit performs a reset operation to initialize each detection element by using each reset unit.
For example, in an operation mode of repeatedly performing radiation imaging such as continuous shooting or movie capturing, the driving unit repeatedly performs a reset operation and an output operation of outputting sensor signals. One image data formed based on sensor signals obtained by such a series of operations is also called a “frame”, and the quantity of image data obtained per unit time is also called a “frame rate”. For example, when performing movie capturing, increasing the frame rate will smoothly play back a movie.
Japanese Patent Laid-Open No. 2012-85124 discloses an arrangement in which each sensor unit includes a sampling unit which samples sensor signals in addition to a plurality of sensors and a driving unit. Upon sampling a sensor signal, each sampling unit holds the sampled sensor signal until it samples the next frame. Therefore, after each sampling unit samples a sensor signal, the corresponding driving unit can perform an output operation of outputting the sampled sensor signal at an arbitrary timing. According to Japanese Patent Laid-Open No. 2012-85124, when starting, during an output operation for a given frame, a reset operation for the next frame, each driving unit interrupts the output operation and resumes the interrupted output operation upon finishing the reset operation.
According to the driving method disclosed in Japanese Patent Laid-Open No. 2012-85124, it is possible to shorten the intervals between radiation imaging operations to be repeatedly performed, when starting, during an output operation for a given frame, a reset operation for the next frame. This can increase the frame rate. In addition, according to the driving method disclosed in Japanese Patent Laid-Open No. 2012-85124, since no output operation is performed during the execution of a reset operation, it is possible to reduce the influence of noise originating from the reset operation on the image data obtained by the output operation.
A sensor signal contains a noise component originating from a dark current or the like in addition to a signal component. The noise component is based on the time from the end of a reset operation to the start of sampling of the sensor signal. For this reason, according to the driving method disclosed in Japanese Patent Laid-Open No. 2012-85124, there is a difference in noise component between a sensor signal output (by an output operation before interruption) before the start of a reset operation for the next frame and a sensor signal output (by an output operation after resumption) after the end of the reset operation. This can cause contrast unevenness as noise on the radiation image formed based on image data.
This can cause a problem when performing offset correction for removing a noise component originating from a dark current or the like with respect to image data. According to offset correction, a radiation image is formed based on the difference between the radiation image data obtained by imaging with radiation irradiation and the offset image data obtained by imaging without radiation irradiation. In order to properly remove the above unevenness noise by offset correction, it is necessary to perform these two imaging operations under the same imaging conditions (for example, conditions under which the time from the end of a reset operation to the start of sampling of a sensor signal remains the same). According to the driving method disclosed in Japanese Patent Laid-Open No. 2012-85124, since the time before the start of the sampling (that is, the timing of the interruption of an output operation) can changes for each frame, it is necessary to prepare a large amount of offset image data to perform offset correction.